Abstract: Optimal positions of actuators for active control of a trussed structure is studied, where the finite element method is used to establish dynamic equations of the structure, piezoelectric stack is used as an actuator, particle swarm optimizer (PSO) is adopted as the optimization algorithm and the energy-based controllable Gramian matrix is used as optimization criteria. Iterative algorithm of the PSO is presented and the mechanism of controllable Gramian matrix is analyzed. Dynamic responses of the structure under white noise and simple harmonic excitations are both numerically studied using the optimal control method. Simulation results indicate that the PSO is effective in determining optimal positions of actuators on the structure. The structure may be well controlled by the optimal controller.